This invention relates to the treatment of oil-water emulsions that are produced as a result of tertiary or enhanced recovery operations that employ anionic surfactants.
Surfactant flooding has become one of the more promising enhanced recovery techniques for recovering oil after waterflooding. Generally the method employs the injection of a slug of surfactant such as a petroleum sulfonate contained in an aqueous medium, followed by a drive fluid such as water. Variations may include following the surfactant slug with an aqueous polymer slug employing a polysaccharide or polyacrylamide for mobility control. In the surfactant flooding enhanced recovery is realized, it is believed, principally because of the effectiveness of the surfactant to reduce the interfacial tension between the crude oil and water. Although anionic, cationic and nonionic surfactants and mixtures thereof have been suggested, the anionic surfactants, and particularly the petroleum sulfonates, have gained the widest recognition as surfactant additives.
The liquids produced as a result of a tertiary recovery operation involving the use of surfactant or micellar flooding are generally oil-water emulsions that are very stable especially since they may contain surfactants such as a petroleum sulfonate which had been injected into the formation as a recovery agent for enhancing recovery of oil therefrom.
While it is desired that the surfactants concentrate at the oil-water interfaces during the flooding operation, under certain conditions the surfactants become more oil-than-water soluble, and thus concentrate in the oil phase. Not only do the surfactants lose their effectiveness but also considerable quantities of surfactants are contained in the produced crude oil. While surfactant flooding has shown promise for enhancing oil recovery, the economics necessary for commercial application require that the costs of the surfactant be minimized.
It is thus an object of the present invention to reduce the expenses related to the surfactant by providing a method for the recovery of the surfactants from the oil phase of the produced emulsion.
It is a further object of this invention to recycle the recovered concentrated surfactant of additional tertiary recovery operations.
It is yet another object of this invention to provide a produced crude oil having reduced surfactant concentration present so that the crude oil may be processed in refining operations without additional pretreatment for removal of the surfactants.